Modern tactical aircraft use a number of imaging aids to assist the crew in viewing a scene, selecting targets in the scene, and directing weapons against the selected targets. Visible, infrared, and/or specific spectral bands imaging devices are used in various applications to form an image of the scene. The type of imaging spectrum detected by electromagnetic instruments depends upon the mission, weather conditions, the nature of the scene, as well as other factors.
Issues associated with airflow over electromagnetic instruments are well known. In a particular example, electro-optical and infrared turrets having viewing window diameters of nine inches or greater suffer electro-optical resolution losses over most of the turret's field of regard due to flow turbulence immediately in front of the window at speeds greater than 120 knots. Reference can be made to U.S. Patent Application Publication No. 2015/0251745 A1, which discloses a device secured to a housing of an optical instrument to improve airflow over the optical instrument.
FIG. 1 illustrates an annular air foil 60 mounted on the spherical cover 30 of the housing 10 in a position that the air foil surrounds a window 12 to control fluid flow over the window. The air foil 60 includes an annular body having an inner peripheral edge and an outer peripheral edge. The body of the air foil 60 further includes an arcuate outer surface disposed between the inner peripheral edge and the outer peripheral edge. The air foil 60 shown in FIG. 1 embodies a complete air foil. Airborne electro-optical/infrared turrets have been fitted with air foils in order to improve optical performance. However, these air foils generate excessive aerodynamic torque when the turret is looking aft. Aerodynamic torque limits the operational airspeed. The trend is to place these turrets on faster and faster platforms.